Total electron content at equatorial and low-, middle- and high-latitudes in African longitude sector and its comparison with IRI-2016 and IRI-PLAS 2017 models

Abstract

Ionosphere plays crucial role in satellite communication as well as the modern space-based positioning, navigation and timing applications. Progressive exploitation of ground and space-based observations across the African region has relatively strengthened the understanding and modeling of spatiotemporal ionospheric variations over the territory. However, it is also equally important to understand the latitudinal behaviour of ionosphere over the African longitude that would reinforce the ionospheric delay error modelling practices for an improved radio communication along the satellite pass. Hence, the aim of this research is to investigate the diurnal, seasonal and latitudinal variations of global positioning system derived total electron content (GPS-TEC) and to assess the performance of the recent version of empirical international reference ionosphere (IRI-2016) and plasmaspheric IRI (IRI-PLAS 2017) models during the ascending phase of solar cycle 24 (2012). The study is also supported by the integrated ionospheric TEC (IONO-TEC) extracted from the Digisonde observations in the vicinity of GPS receiver locations. The 3 GPS stations considered in this study are at a) an equatorial/ low-latitude location Federal University of Technology, Yola (FUTY; 9.35°N, 12.50°E, 4.91°S dip), b) a mid-latitude location Ankara (ANKR; 39.89°N, 32.76°E, 57.62°N dip), and a high-latitude location Tromso (TRO1; 69.66°N, 18.94°E, 78.17°N dip) in the northern hemisphere. Observations show the magnitude of TEC generally decreases with increasing latitude. While the average diurnal maximum of GPS-TEC at equatorial and low-latitude follow an almost equal level of magnitude during March and September equinoxes, the observations at middle and high latitude stations presents the highest magnitudes during the September equinox. Moreover, we noticed obvious higher magnitude of GPS-TEC than IONO-TEC at the three stations suggesting the discrepancies could be corresponding to the topside modeling and plasmaspheric contributions. The other prominent feature is the pattern of diurnal TEC being dome shaped at middle and high latitude locations whereas the equatorial and low latitude location manifested a noon bite-out characteristic in the IONO-TEC, IRI-2016, and IRI-PLAS outcomes. The comparative analysis of IRI-2016 and IRI-PLAS 2017 estimated TEC with the GPS-TEC show a clear overestimation of IRI-PLAS 2017 outcomes irrespective of seasons and latitudinal locations whereas the IRI-2016 outcomes either overestimated or underestimated the GPS-TEC. Hence, this study reveals that IRI-2016 performs better predictions compared to IRI-PLAS 2017 at all the three latitudinal locations. Such a latitudinal comparison across the African-European longitudinal sector may complement towards the efforts for improving the regional as well as global ionospheric model performances.